media: rcar-vin: Fold interrupt helpers into only callers

The call sites using the interrupt helper functions have all been
reworked to only one for each. Fold each of them into the only call
sites left.

This fixes a possible interrupt loss in case an interrupt occurs between
reading VNINTS_REG in rvin_get_interrupt_status() and reading it again
in rvin_ack_interrupt().

While at it rename the variable holding the current interrupt status to
make the code easier to read.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250616185722.980722-2-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>